This invention relates to gate drive circuit for a thyristor deflection system.
It is common to derive the trace thyristor gate drive signal from a tap or winding associated with the input reactor as disclosed in U.S. Pat. No. 3,452,244. However, when certain types of regulators, such as controlled switching devices in series with the input reactor are used, the waveforms of the reactor are no longer suitable for direct use as drive signals.
It has been common practice to manufacture television receivers without using a separate line transformer for isolating the receiver chassis from the alternating current source in order to save the cost of such a transformer. In such a situation, the receiver chassis will be floating, that is, tied to the alternating current line. With suitable precautions taken to ensure that the receiver chassis is insulated so that the user will not come into electrical contact with the chassis there is vitually no danger of electrical shock to the user. However, with the advant of devices such as video recorders which may be adapted to record and playback signals with the television receiver it is necessary to isolate the receiver from the alternating current line so that the recording unit may be electrically connected to the receiver chassis ground.
In copending United States Application Ser. No. 460,648, entitled "Alternating Current Line Voltage Supply Isolation Using Deflection System Output Transformer", several arrangements are disclosed for utilizing the horizontal deflection output transformer for achieving line isolation. The disclosed arrangements are suitable for use in deflection systems including the dual bi-directional conducting thyristor deflection system described in U.S. Pat. No. 3,452,244. With such arrangement either the secondary circuits of the output transformer may be referenced to chassis ground or also the trace switch may also be referenced to chassis ground thereby minimizing the insulation necessary to separate the viewer from the chassis while eliminating the requirement of a separate line isolation transformer.
Of concern in any isolation scheme including that described in the aforementioned application is the number of connections between the isolated and non-isolated portions of the receiver. From a point of view of safety and lack of complexity, it is desirable to minimize the number of these connections.